Motor starters consist of two devices—a contactor that completes the circuit to the motor and an overload relay that monitors the current the motor is drawing. … When a condition occurs that causes the motor to exceed the maximum load, the device opens the motor starter control circuit and the motor is turned off.
What are contactors motor starters?
A motor starter is simply a contactor PLUS an overload relay and is rated by motor HP or amperage. If there is no overload relay it is not a starter any longer. It’s back to being just a contactor. The starter employs overload relays to protect the motor from load surges by shutting it down to prevent overheating.
What are the difference of motor starter relays and contactors?
A Motor Starter is a basically a contactor with the addition of an overload relay which will drop out the coil voltage in case of motor overload condition. A Contactor is an electrically control switch same as a relay. It is used for switching the current to ON and OFF a circuit.
What does a motor starter have that a contactor does not have?
The difference is that motor starters have one extra system or systems not found in contactors — an overload relay of some type to cut voltage input should that relay sense a motor-overload or thermally compromising condition due prolonged running overcurrent.
How does a coil on a motor starter work?
When the coil is energized, this creates a magnetic coupling between the contacts & contact carrier, allowing them to stay together and current to flow to the motor or other load until the system is shut off by de-energizing the coil.
What is the main difference between a relay and a contactor and between a contactor and a magnetic motor starter?
Comparison of Relay and Contactors
|Relays are switching devices used in any control circuit for checking a condition or multiplying the number of contacts available.||Contactors are switching devices used to control power flow to any load.|
|Relatively smaller in size||Larger when compared to Relays|
What is the difference between a motor starter and a contactor quizlet?
Terms in this set (15)
What is the difference between a motor starter and a contactor? The motor starter has an overload relay. … In this circuit, the HR contactor is equipped with five contacts. Three load contacts and two are auxiliary contacts.
What is the purpose of coil clearing contacts?
What is the purpose of coil-clearing contacts? They are used with latching relays to prevent power being maintained to a coil after it has energized.
Why is starter used in starting of DC motor?
Starters are used to protect DC motors from damage that can be caused by very high current and torque during startup. They do this by providing external resistance to the motor, which is connected in series to the motor’s armature winding and restricts the current to an acceptable level.
What are the two main electrical parts of a relay or contactor?
The contacts are the current-carrying part of the contactor. This includes power contacts, auxiliary contacts, and contact springs. The electromagnet (or “coil”) provides the driving force to close the contacts. The enclosure is a frame housing the contacts and the electromagnet.
Why do I need a contactor?
A contactor is an electrical device which is used for switching an electrical circuit on or off. … These contacts are in most cases normally open and provide operating power to the load when the contactor coil is energized. Contactors are most commonly used for controlling electric motors.
Do contactors have overload protection?
Contactors are used to control power in a variety of applications. When applied in motor-control applications, contactors can only start and stop motors. Contactors cannot sense when the motor is being loaded beyond its rated conditions. They provide no overload protection.
How do you select a motor contactor?
As per above chart:
- Type of Contactor = AC7b.
- Size of Main Contactor = 100%X Full Load Current (Line).
- Size of Main Contactor = 100%x6 = 6 Amp.
- Making/Breaking Capacity of Contactor = Value above Chart x Full Load Current (Line).
- Making/Breaking Capacity of Contactor = 8×6 = 52 Amp.
Why is it not a good idea to file or sand the contactor contacts?
Why is it not a good idea to file or sand the contactor contacts? Filing or sanding exposes the base metals under the silver plating and speeds deterioration.
How does the magnetic contactor operate?
Working principle of a magnetic contactor
Magnetism is activated by the current -flowing through the coil- and the two magnetism come closer to each other. This movement turns off the two magnetism. Therefore, the contacts close, and the springs provide power to the contacts.
What is the function of auxiliary contacts in a magnetic motor starter?
When an overload is detected, the auxiliary contact of the overload relay opens the circuit and prevents the motor from burning out or overheating. Electronic or electromechanical overload relays are used in combination with a contactor to provide the required overload protection.